Osmotic therapeutic systems manufactured in the form of osmotic devices for the precision administration of drugs with control of delivery patterns, and with extended operational delivery times are known in U.S. Pat. Nos. 3,845,770 and 3,916,899 both issued to inventors Felix Theeuwes and Takeru Higuchi. The osmotic systems disclosed in these pioneer patents are made of a semipermeable wall that surrounds a reservoir containing durg. The wall is permeable to the passage of an external fluid, impermeable to the passage of drug, and it has a passageway through the semipermeable wall for delivering drug from the osmotic system. These systems are extraordinarily effective for delivering a drug that is soluble in the fluid, and also for delivering a drug that has limited solubility in the fluid and is mixed with an osmotically effective compound that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid. The osmotic systems release drug by fluid being imbibed through the semipermeable wall into the reservoir at a rate determined by the permeability of the semipermeable wall and the osmotic pressure gradient across the wall producing a solution of soluble drug, or a solution of soluble compound containing drug, which solution in either operation is delivered at a controlled rate over a prolonged period of time.
An unobvious and unexpected advance was made in osmotic systems by patentees Felix Theeuwes and Atul D. Ayer as disclosed in U.S. Pat. Nos. 4,008,719; 4,014,334; 4,058,122; 4,116,241; 4,160,452; and 4,256,108. In these patents, the patentees provided osmotic systems comprising a laminated wall formed of two laminae, a semipermeable lamina and a microporous lamina, that act in cooperation to provide improved controlled delivery of drug over a prolonged period of time. The two laminae maintain their physical and chemical integrity during the controlled dispensing of drug, and the laminate allows a wider control over the rate at which drug is delivered to a drug receptor site over a prolonged period of time.
While the above osmotic systems comprising a single layer semipermeable wall, and the osmotic systems comprising the laminated wall consisting of a semipermeable lamina and a microporous lamina represent outstanding and pioneering advancements in the osmotic delivery art, and while they are useful for dispensing innumerable drugs to the environment of use, it has now been discovered these osmotic systems can be improved further to enhance the drug delivery kinetics and the usefulness of the osmotic systems. That is, it has now been discovered unexpectedly that osmotic systems can be provided that initially deliver a bio-affecting drug in an increased amount followed by a substantially constant amount at a controlled rate over time; thereby, making drug available instantly to a drug receptor by substantially eliminating the start-up drug delivery time frequently required to deliver some drugs by osmotic systems. The therapeutic osmotic systems made available by this invention embodying the unique initial drug delivery followed by controlled and constant prolonged delivery, thereby function according to a pre-selected built-in optimal program of drug presentation.